EP0427646A1 - Method of manufacturing extruded profiles of thermotropic polymers and the industrially usable profiles obtained in such a way - Google Patents

Abstract

Process for the manufacture of profiles suitable for a subsequent industrial use, from thermotropic polymers which are capable of forming anisotropic melts. This process is carried out by performing an extrusion operation which is known to a person skilled in the art, but by choosing particular temperature conditions according to which the molten polymer at a temperature T1 higher than the melting temperature TM (at which the liquid crystal phase appears) is cooled before it enters the die at a temperature T2 lower than TM. The present invention also relates to profiles made from thermotropic polymers and whose close structure is nonfibrillar. The profiles obtained can be, in particular, granulated and then ground to produce fine and pourable powders which are suitable, for example, for electrostatic coating.

Description

The present invention relates to a process for preparing profiles which can be used industrially from thermotropic polymers which are capable of forming anisotropic melts, said process consisting in carrying out an extrusion operation having a special temperature profile. The present invention also relates to profiles, capable of being obtained at the end of this process, having an intimate non-fibrillar structure.

Over the past ten years, there has been an increasing interest in polymers which are capable of forming anisotropic melts; we also speak of polymers which are capable of forming molten phases of liquid crystal (or organized mesophase). These polymers have different phase transition temperatures which are, in ascending order of temperatures:
- the crystallization temperature on cooling (T _c );
- the melting temperature (T _F ) at which the liquid crystal phase appears; and
- the clarification temperature (T _cl ) above which the mesophase becomes isotropic. These temperatures T _c , T _F and T _cl are determined by differential scanning calorimetry (DSC), using a DU PONT device comprising a DSC 910 module coupled to a central processing unit 9900, on samples subjected to temperature variations both up and down 20 ° C / minute; the crystallization and melting temperatures correspond to the peaks of the cooling crystallization exotherm and the melting endotherm. The nature of the phases present is identified by observations using a polarizing microscope equipped with a heating plate. The temperature range of the anisotropy range, the interval which can be represented by the difference T _cl - T _F and which has a value ranging from ten degrees to several tens of degrees, will depend essentially on the structure of the thermotropic polymer.

Interest in the thermotropic polymers we talked about above is linked to the fact that these polymers spontaneously have in the molten state their own orientation and a relatively high degree of organization. This orientation and this organization are found in the shaped objects obtained from these polymers by conferring on them improved physico-chemical and mechanical properties which are not observed on identical but isotropic objects. However, given this spontaneous orientation and organization of the material in the molten state, the transformation of these thermotropic polymers by extrusion:
- when it comes to making different objects of son and fibers and consisting of profiles such as rods, bars and tubes,
said extrusion being carried out according to the usual known operating method and used by a person skilled in the art for extruding non-thermotropic polymers in which the temperature of the polymeric material which is chosen, both in the body of the extruder and in the die calibration, is located at a value higher than the polymer melting temperature (in the case of a thermotropic polymer, this value is generally situated in the anisotropy range),
leads to shaped objects whose intimate structure, even after cooling, is highly fibrillar due to the essentially uniaxial orientation of the polymer chains in the direction of flow of the material; consequently, such extruded objects, which have a transverse embrittlement generating delamination phenomena, cannot be suitable for subsequent industrial use.

If, for example, it is a rod that is recovered at the end of the chain, we have found that it is still impossible, if not very difficult, to obtain:
- when a granulation operation is carried out under conventional conditions known and used by those skilled in the art to granulate a rod made of non-thermotropic polymer,
- compact granules of intimate non-fibrillar structure which allow on the one hand the good performance of a subsequent grinding operation under these conventional conditions and on the other hand the recovery of a grinding product in the form of fine and pourable powders which one knows the interest for applications such as for example electrostatic coating or in a fluidized bed, the production of thermoplastic composites by compression molding. The powders based on thermotropic polymer obtained consist of particles which are not spherical but acicular in shape, and these powders constitute a flock (or tangle) of non-flowable microfibrils, that is to say a set of fibers of very diverse sizes also not flowable.

In a first object, the present invention aims precisely to provide a process for the production of profiles suitable for subsequent industrial use, from thermotropic polymers, which is carried out by carrying out an extrusion operation and by using conventional apparatus or devices known and used by those skilled in the art for the extrusion of non-thermotropic polymers, but by choosing particular temperature conditions for the conduct of the extrusion.

In a second object, the invention aims to provide profiles, in thermotropic polymer, suitable for later industrial use, the intimate structure of which is not fibrillary: these profiles are capable of being obtained by the process in accordance with first object of the invention.

It has now been found that it is possible to achieve all of the goals defined above thanks to the implementation of the method, the definition of which will follow.

More specifically, the present invention, in its first object, relates to a process for the preparation by extrusion of profiles suitable for subsequent industrial use from thermotropic polymers which are capable of forming anisotropic melts, said process comprising the following steps:
. the formation in an extruder of a polymer material in the fluid state,
. the passage of the material in the fluid state through a calibration die of suitable shape,
said process being characterized in that:
the thermotropic polymer melted at a temperature T₁ higher than the melting temperature T _F at which the liquid crystal phase appears,
- is cooled before entering the die so as to reach, at the latest at the time of entry into the die, a temperature T₂ between a value which is 7 ° C lower than the temperature T _F and a minimum value which is equal to the crystallization temperature T _c ,
- Then it is maintained at said temperature T₂ during its passage through the die and, possibly, until it enters an apparatus or a device placed outside the die and used in the context of industrial use. subsequent formed profiles.

By "profile" is meant according to the present invention to describe:
- solid cylindrical profiles which can be either linear rods of uniform cross-section in the form of various shapes as well as possibly linear bars of uniform cross-section of various forms,
- hollow cylindrical profiles which may be possibly linear tubes of uniform section of various shapes.

A preferred embodiment of the invention consists in producing linear rods having a uniform circular section with a diameter ranging for example from 1 to 6 mm.

It should be noted that the profiles obtained can be stored without ambient air before using them in subsequent industrial packaging operations such as, for example, granulation and grinding operations.

By the expression "extruder" is meant a device which does not have a dead zone during the progression of the material. Devices of this kind are well known to those skilled in the art and they may include one or more screws. A preferred embodiment of the invention consists in using an extruder whose size and kneading members are studied so as not to induce self-heating of the polymeric material which is worked. As examples of devices that can be used, mention may be made of the single-screw extruders commercially available under the brands: BRABANDER, PRODEX, SAMAFOR and THORET; the twin-screw extruders commercially available under the brands: BUSS, ZSK and LEISTRITZ.

Thermotropic polymers capable of forming anisotropic melts which are suitable for carrying out the process according to the present invention, taken in its first object, include polyesters fully aromatic, alkyl aromatic polyesters, fully aromatic polyester amides, alkyl aromatic polyester amides, aromatic polyazomethines, aromatic polyester carbonates and mixtures of these polymers.

According to a preferred embodiment of the process according to the present invention, the thermotropic polymers which are used are fully aromatic polyesters, fully aromatic polyesteramides and mixtures of these polymers.

Totally aromatic thermotropic polyesters are described for example: in US patents US-A-3,991,013, 3,991,014, 4,066,620, 4,075,262, 4,118,372, 4,130,545, 4,161,470, 4,181,792, 4,188,476, 4,219,461, 4,224,433, 4,230,817, 4,346,208; in European patent application EP-A-0.191.705; and in French patent application FR-A-2,617,851: the substance of these patents or patent applications is incorporated here by reference.

Totally aromatic thermotropic polyesteramides are described, for example: in US patents US-A-4,272,625, 4,330,457, 4,339,375, 4,355,132; in European patent application EP-A-0.272.992; and in French patent applications FR-A-2,617,851, 2,617,852 and 2,617,853; the substance of these patents or patent applications is incorporated here also by reference.

The thermotropic polymers which are advantageously chosen for the implementation of the present invention are those, belonging to the above-mentioned general or preferred families, which have a melting point in the range from 200 ° C to 370 ° C and, preferably ranging from 260 ° C to 350 ° C and which have an inherent viscosity at least equal to 0.5 dlg⁻¹ and preferably lying in the range from 1.0 to 4.0 dlg⁻¹. Regarding the inherent viscosity, it should be specified that it is measured at 25 ° C. on a solution containing 0.5 g of polymer per 100 cm³ of solvent (s) such as for example the mixture parachlorophenol / 1,2-dichloroethane ( 50/50 by volume).

dans laquelle
R₁ représente un radical méthyle ou éthyle ou un atome de chlore ou de brome, les unités (I) pouvant être identiques ou différentes entre elles,

dans laquelle le symbole A représente un atome d'oxygène ou le groupement NH ;
- le rapport molaire des unités (I) par rapport à la somme des unités (II) + (III) se situe dans l'intervalle allant de 0,95 à 1,05 ;
- la quantité des unités (II) dans le mélange (II) + (III) se situe dans l'intervalle allant de 0 à 70 % en mole et celle des unités (III), par rapport à la même référence, se situe dans l'intervalle allant de 100 à 30 % en mole ;
- la quantité des unités (IV), exprimée par rapport à la quantité des unités (I), se situe dans l'intervalle allant, dans le cas où A = 0, de 10 à 300 % en mole et, dans le cas où A = NH, de 5 à 100 % en mole.Fully aromatic thermotropic polyesters and polyesteramides which are especially preferred for the implementation of the present invention are those described in European patent applications EP-A-0.191.705 and 0.272.992. These polyesters and polyesteramides have the following features:
they include recurrence units of formula (I), (II), (III) and (IV), the presence of the units (II) being optional:
(I) designating the structure:

in which
R₁ represents a methyl or ethyl radical or a chlorine or bromine atom, the units (I) possibly being identical or different between them,

in which the symbol A represents an oxygen atom or the NH group;
- The molar ratio of the units (I) to the sum of the units (II) + (III) is in the range from 0.95 to 1.05;
- the quantity of the units (II) in the mixture (II) + (III) is in the range from 0 to 70 mol% and that of the units (III), relative to the same reference, is in the range from 100 to 30 mol%;
- the quantity of the units (IV), expressed in relation to the quantity of the units (I), lies in the interval going, in the case where A = 0, from 10 to 300 mol% and, in the case where A = NH, from 5 to 100% by mole.

According to an even more particularly preferred form, the thermotropic totally aromatic polyesters and polyesteramides which can be used in the present invention have a structure such as that defined above in which:
- the quantity of the units (II) in the mixture (II) + (III) is in the range going from 20 to 60 mol% and that of the units (III), compared to the same reference, goes from 80 40% by mole,
- and the quantity of the units (IV), expressed in relation to the quantity of the units (I), is in the range ranging, in the case where A = 0, from 30 to 200% by mole and, in the case where A = NH, from 10 to 60 mol%. Among the polyesters and aromatic polyesteramides corresponding to this even more especially preferred modality, those which are very suitable are polymers having a structure in which the units (I) are identical, with the substituent R₁ representing a methyl radical or a chlorine atom.

où R₂ et R₃, qui peuvent être identiques ou différents, ont chacun la définition donnée ci-avant pour R₁, les unités (I˝) pouvant être identiques ou différentes entre elles,

où le symbole A a la signification donnée ci-avant à propos des unités (IV).The completely preferred thermotropic completely aromatic polyesters and polyesteramides which have just been mentioned also include polymers which may also contain in their structure aromatic units generating ester and amide functions (dioxy units and / or dicarbonyl units and / or mixed oxy units / carbonyl or amino-secondary / carbonyl) having a structure other than that of units (I), (II), (III) and (IV), the total amount of these additional units being at most equal to 10 mol% per relative to the quantity of units (I). A non-exhaustive list of these additional units is as follows:

where R₂ and R₃, which can be identical or different, each have the definition given above for R₁, the units (I˝) being able to be identical or different between them,

where the symbol A has the meaning given above in connection with the units (IV).

- la quantité des unités (V) dans le mélange (V) + (VI) se situe dans l'intervalle allant de 10 à 90 % en mole et celle des unités (VI), par rapport à la même référence, se situe dans l'intervalle allant de 90 à 10 % en mole ;
. S'agissant des polyesteramides :
- ils comprennent des unités de récurrence de formules (VII), (VIII) et (IX) :

- la quantité des unités (VII) dans le mélange (VII) + (VIII) + (IX) se situe dans l'intervalle allant de 10 à 90 % en mole, celle des unités (VIII), par rapport à la même référence, se situe dans l'intervalle allant de 5 à 45 % en mole et celle des unités (IX), par rapport à la même référence, se situe dans l'intervalle allant de 5 à 45 % en mole.Another type of completely aromatic thermotropic polyesters and polyesteramides which are also very particularly preferred for the implementation of the present invention consists of the polymers described in American patents US-A-4,161,470 and 4,330,457 which have the following features :
. Regarding polyesters:
- they include recurrence units of formula (V) and (VI)

- the quantity of the units (V) in the mixture (V) + (VI) is in the range from 10 to 90% by mole and that of the units (VI), with respect to the same reference, is in the range from 90 to 10 mol%;
. With regard to polyesteramides:
- they include recurrence units of formulas (VII), (VIII) and (IX):

- the quantity of units (VII) in the mixture (VII) + (VIII) + (IX) is in the range from 10 to 90% by mole, that of the units (VIII), relative to the same reference , is in the range from 5 to 45% by mole and that of the units (IX), with respect to the same reference, is in the range ranging from 5 to 45% by mole.

Among the completely aromatic polyesters and polyesteramides belonging to this other group of very especially preferred polymers, those which are very suitable are the polymers placed on the market by the company CELANESE, under the registered trademark VECTRA, of type A 900 (polyester) or B 900 (polyesteramide).

As already mentioned above when defining the present invention, taken in its first object, an essential condition for the implementation of the process envisaged here consists in the establishment in the extruder of temperature conditions particular.

The temperature T₁ is chosen so as to avoid any phase heterogeneity in the melt. This temperature is a function of the shear rate and duration, but it is at least 5 ° C higher than the melting temperature T _F at which the liquid crystal phase appears. The difference between T₁ and T _F is higher the higher the ability to crystallize the polymer and the higher the extrusion rates. Preferably, the thermotropic polymer is melted at a temperature T₁ between a value greater than 5 ° C at T _F and the clarification temperature T _cl , taking care however not to exceed for T₁ a value equal to T _F + 50 ° vs. The difference T _cl - T _F is variable depending on the type of polymer, and it can commonly reach 20 to 60 ° C.

The cooling of the melt to the temperature T₂ is carried out in a homogeneous manner, that is to say that not only the surface layers but also the entire vein in the fluid state must be brought, at the latest at time of entry into the die, at the chosen cooling temperature. The cooling conditions and the extrusion rate must also be controlled so as to avoid self-heating of the polymeric material. In particular, the temperature of the molten extrudate should not be lowered to a temperature below the crystallization temperature T _c . It is essential that cooling takes place before entering the die so that the entire vein in the fluid state can be at the temperature T₂ chosen when said vein passes through the die. Preferably, the temperature T₂ is chosen to be between a value which is 7 ° C lower than the temperature T _F and a value which is 10 ° C higher than the crystallization temperature T _c . The difference T _F - T _c is variable and it can be between 20 and 40 ° C. Even more preferably, the temperature T₂ is chosen to be between a value which is 7 ° C lower than the temperature T _F and a value which is 15 ° C higher than the temperature T _c .

In the case where the amplitude of the cooling is not very large, for example of the order of a few degrees to about thirty degrees, the cooling can be achieved by varying the flow rate of the material to be extruded. It is also possible to use an extruder equipped with a very long screw in which the molten material cools as it progresses towards the end of the screw.

According to another embodiment, the cooling to the desired temperature is carried out before passing through the die using a cooler-homogenizer device interposed between the end of the barrel of the extruder and the calibration die. A simple type of device, usable for the implementation of the invention, can be found in static or dynamic mixers which offer the advantage of allowing efficient and homogeneous heat exchange without high pressure drop and of being able to be adapted, by a suitable choice of the number, the geometry and the temperature of the elements, the amplitude of the cooling to be carried out. More details on this device can be found in French patent FR-A-2,373,385.

Let us return now to the profiles which are obtained at the exit of the die.

The present invention, in its second object, also relates to such profiles as product-per-se, that is to say independently of the process described so far which is likely to be used to prepare them.

These thermotropic polymer profiles are characterized in that they have an intimate isotropic (possibly weakly anisotropic) non-fibrillar structure. It corresponds to the so-called isotropic state (which can be weakly anisotropic) of their structure a rate of crystalline orientation fc which is equal to or less than 0.3; this measurement of the crystal orientation rate fc is carried out by X-ray diffraction on a PHILIPPS PW -1130/1300 apparatus according to the method described in the work "Principles of Polymer Processing" by Z. TADMOR and CG GOGOS, published by editions J. WILEY AND SONS in 1979, pages 77 to 80: we recall that a rate fc equal to 1 corresponds to a completely anisotropic intimate structure (or perfectly oriented structure), while a rate fc equal to zero corresponds to a totally isotropic intimate structure (or perfectly disoriented structure).

At the exit of the die, the profiles obtained are generally already defined on one or two dimension (s). In the context of the subsequent industrial use of these profiles, they can be taken over by machines which direct them to apparatus or devices which will ensure their final packaging. Depending on the case, the profiles can be: granules then crushed, rolled up, passed through a shaper, stretch-blown, etc.

If, for example, the extruded product is a linear rod, having a uni-circular section with a diameter ranging from 2 to 6 mm, then compact granules can be obtained by granulation having dimensions for example in a direction between 2 mm and 6 mm and in the other direction between 2 mm and 12 mm.

These compact granules of thermotropic polymer are characterized in that they each have an intimate structure which is also isotropic (possibly being weakly anisotropic) non-fibrillar. There also corresponds to said isotropic state (which can be weakly anisotropic) of their structure, a rate of crystalline orientation which is equal to or less than 0.3.

These granules allow the success of the subsequent grinding operation to be carried out under completely conventional conditions. The grinding product is a fine, pourable powder characterized in that, on the one hand, it consists of particles of spherical shape and, on the other hand, said particles each also have an intimate isotropic (possibly weakly anisotropic) non-fibrillar structure.

The following example is given without limitation and shows how the present invention can be practiced.

EXAMPLE AND COMPARATORY TESTS: 1. Description of the thermotropic polymer used:

An aromatic copolyester of the type described in European patent application EP-A-0.191.705 is prepared.

• (1) diacétate de méthylhydroquinone : 64,10 kg
  rapport molaire (1)/(2) + (3) = 1
• (2) acide téréphtalique : 26,77 kg
  50 % en mole dans mélange (2) + (3)
• (3) dicarboxy-4,4′ diphényléther : 41,61 kg
  50 % en mole dans mélange (2) + (3)
• (4) acide para-acétoxybenzoïque : 34,84 kg
  60 % en mole par rapport à (1).

The following reagents are introduced into a 300 liter polycondensation reactor stirred and heated by a heat transfer fluid circulating in the double jacket of the reactor, equipped with a device for distillation and sweeping with an inert gas:

• (1) methyl hydroquinone diacetate: 64.10 kg
  molar ratio (1) / (2) + (3) = 1
• (2) terephthalic acid: 26.77 kg
  50% by mole in mixture (2) + (3)
• (3) dicarboxy-4,4 ′ diphenyl ether: 41.61 kg
  50% by mole in mixture (2) + (3)
• (4) para-acetoxybenzoic acid: 34.84 kg
  60% by mole relative to (1).

The reactor is purged with nitrogen, then heated by the heat transfer fluid adjusted to 260 ° C for 2 hours; this temperature is then brought to 300 ° C. for 20 minutes. The amount of distilled acetic acid is 42.82 kg (85% of theory). The temperature of the heat transfer fluid is then gradually raised to 310 ° C in 60 minutes, at the same time reducing the pressure from 1010.10² Pa to 2.66.10² Pa. The temperature is still maintained at 310 ° C and the pressure 2.66.10² Pa for 10 minutes; the amount of acetic acid collected during this step is 7.55 kg (totaling 100% of theory).

Stirring is then stopped, then a nitrogen pressure is established in the reactor and the polymer is drawn off at 310 ° C through a circular valve 8 mm in diameter. The polymer obtained is recovered in the form of a grayish rod, of non-uniform more or less circular section, having a fibrillar structure: this rod is cooled by immersion over a length of 2 meters in water maintained at 17 ° C., then it is cut into non-compact granules (they have an intimate fibrillar structure) of heterogeneous shape and dimensions using a granulator available in the trade under the AUTOMATIC brand.

The polymer obtained has an inherent viscosity of 1.93 dlg⁻¹ (solvents: parachlorophenol / 1,2-dichloroethane, 50/50 by volume). The crystallization temperature T _c is equal to 267 ° C. The melting temperature T _F at which the liquid crystal phase appears is equal to 300 ° C. The clarification temperature T _cl above which the mesophase becomes isotropic is greater than 350 ° C.

2. Preparation of a profile according to the invention consisting of a rod of circular uniform section:

The thermotropic polymer is extruded in an extruder with double co-rotating screws of the LEISTRITZ brand comprising screws each having a diameter D equal to 34 mm and a length equal to 35 D.

This extruder is equipped with 10 heating zones for the barrel and a die equipped with a circular hole of 4mm in diameter.

The temperature profile of the material extruded along the sheath is balanced, under regular operating conditions, as indicated below:
- extruder:
. first part where the fusion takes place: it corresponds to zones 1 to 4 where the temperature reaches 320 ° C (temperature T₁):
. second part where the cooling takes place:
* it corresponds to zones 5 to 9 where the temperature gradually increases from 320 ° C to 290 ° C,
* then in zone 10 where the temperature is stabilized at 290 ° C (temperature T₂):
- industry: 290 ° C.

The screw rotation speed is fixed at 100 revolutions / minute and the material flow rate is around 10 kg / hour.

At the outlet of the die, a rod is recovered which has a uni-circular section having a diameter of 4 mm.

3. Subsequent industrial use of the rods obtained:

By way of example of such a use, the operations carried out with the aim of producing, from rods according to the invention, compact granules as well as fine and pourable powders.

Initially, the rod obtained at the outlet of the die is cooled by a path in the air of 5 meters, then it is cut into compact granules each having a diameter of 4 mm and a length of the order of 5 mm, using a granulator with rotary knives of COSTE-CHEVALEYRE brand, type CJ-15-F.

In a second step, a grinding operation is carried out by linking the following two steps:
- A first step in which the compact granules obtained undergo a pre-grinding by operating in a pin impact percussion mill available commercially under the brand ALPINE, type 160 Z; the (linear) speed of rotation of this device is 1.75 m / second and the powder flow rate is around 30 kg / hour:
- A second step in which the powder from the previous pre-grinding is then taken up in an air jet mill with a fluidized bed commercially available under the brand ALPINE type AFG 200; the grinding is carried out with an air pressure of 6.10⁵ Pa, with a selector speed of 9000 revolutions / minute and a product feed rate of 40 kg / hour.

4. Comparative tests A to C:

By way of comparative tests, the same operations were reproduced as those described above in paragraphs 1 to 3, but by modifying in the extrusion pipe the temperature profile of the extruded material. More precisely :
- in test A: the thermotropic polymer melted at temperature T₁ does not undergo any cooling with its entry into the die (the temperature T alors then remains equal to T₁;
- in test B: the thermotropic polymer is brought to a temperature T₁ which is not higher than the melting temperature T _F ;
- in test C: the thermotropic polymer is brought to the appropriate temperature T₁, but insufficient cooling is carried out so that the temperature T₂ is not brought to a value which is at least 7 ° C lower than the temperature T _F.

5. Affected controls and measures:

In each of the examples and tests carried out, the following checks and measurements are carried out, both at the level of the extruded rod and that of the granules and powder:
- visual observations and using a microscope of the intimate structure: it is fibrillar (= F) or non-fibrillar (= NF);
- measurement of the crystal orientation rate fc.

With regard to the powder, we also examine:
- the shape of the particles which constitute it: this shape is spherical (= S) or acicular (= A);
- and its particle size using a laser diffraction particle size analyzer sold under the brand MALVERN: we will give the interval in µm in which the particle diameters are located (= d), with in the case of acicular particles an indication about their average length (= 1 avg).

The following table shows the results of the checks and measurements carried out: EXAMPLE / TEST EXTRUSION TEMPERATURE JUNC, GRANULES AND POWDERS POWDER T1 T2 Faculty Structure Orientation rate Particle shape Granulometry 1 320 ° C 290 ° C 290 ° C NF 0.28 S 10-20 µm AT 310 ° C 310 ° C 310 ° C F 0.95 AT 500-800 µm 1moy ∼ 3d B 280 ° C 280 ° C 280 ° C F 0.70 AT 500-800 µm 1moy ∼ 3d VS 320 ° C 295 ° C 295 ° C F 0.40 AT 300-600 µm 1moy ∼ 2d

Claims (8)

1 / Process for the preparation by extrusion of profiles suitable for subsequent industrial use from thermotropic polymers which are capable of forming anisotropic melts, said process comprising the following steps:
. the formation in an extruder of a polymer material in the fluid state,
. the passage of the material in the fluid state through a calibration die of suitable shape,
said process being characterized in that:
the thermotropic polymer melted at a temperature T₁ higher than the melting temperature T _F at which the liquid crystal phase appears,
- is cooled before entering the die so as to reach, at the latest at the time of entry into the die, a temperature T₂ between a value which is 7 ° C lower than the temperature T _F and a minimum value which is equal to the crystallization temperature T _c ,
- Then it is maintained at said temperature T₂ during its passage through the die and, possibly, until it enters an apparatus or a device placed outside the die and used in the context of industrial use. subsequent formed profiles. 2 / A method according to claim 1, characterized in that the thermotropic polymers which are suitable are fully aromatic polyesters, alkylaromatic polyesters, fully aromatic polyesteramides, alkylaromatic polyesteramides, aromatic polyazomethines, aromatic polyester carbonates and mixtures of these polymers . 3 / A method according to claim 2, characterized in that the thermotropic polymers which are used are fully aromatic polyesters, fully aromatic polyesteramides and mixtures of these polymers. 4 / A method according to any one of claims 1 and 2, characterized in that the thermotropic polymers have a melting temperature in the range of 260 ° C to 350 ° C and having an inherent viscosity in the range of 1 to 4 dlg⁻¹. 5 / A method according to any one of claims 1 to 4, characterized in that:
the thermotropic polymer is melted at a temperature T₁ of between a value 5 ° C higher than the temperature T _F (at which the liquid crystal phase appears) and the clarification temperature T _cl , taking care however not to exceed for T₁ a value equal to T _F + 50 ° C;
- Then is cooled before entering the die so as to reach, at the latest when entering the die, a temperature T₂ between a value which is 7 ° C lower than the temperature T _F and a value which is 10 ° C above the crystallization temperature T _c . 6 / Profiles suitable for subsequent industrial use made from thermostrope polymers capable of forming anisotropic melts, said profiles being capable of being obtained at the end of the process according to any one of Claims 1 to 5, characterized in that they each have an intimate isotropic structure (which may be weakly anisotropic) non-fibrillar. 7 / Profiles according to claim 6, characterized in that it corresponds to the isotropic state (which may be weakly anisotropic) of their structure a rate of crystalline orientation fc which is equal to or less than 0.3. 8 / Use of profiles according to any one of claims 6 and 7, characterized in that, in the context of their subsequent industrial use, they are supported by machines which direct them to the devices or devices which ensure their packaging, packaging according to which they are either granulated and then crushed, or rolled up, or passed through a shaper, or stretch-blown.